Cytosolic free calcium and cell death during metabolic inhibition in a neuronal cell line

Elevated free cytosolic Ca2+ (Ca2+i) has been implicated as a mechanism of hypoxic neuronal death. The calcium hypothesis postulates that the basic metabolic response to hypoxic ATP depletion is a toxic increase in free cytosolic Ca2+i in all cell types. This inherent response then creates the environment in which subsequent derangements of Ca2+i may occur, for example, from glutamate excitotoxicity. Although the effect of glutamate on neuronal Ca2+i has been extensively studied, the basic neuronal response to hypoxia independent of glutamate receptor activation is not well defined. We therefore assayed both Ca2+i and plasma membrane integrity in fura-2-loaded, single SK-N-SH neuroblastoma cells, using digitized video microscopy and metabolic inhibition (2.5 mM NaCN, 10 mM 2-deoxyglucose) to model the ATP depletion of hypoxia. Median time to cell death was 90 min (n = 51 cells). Initial Ca2+i was 121 +/- 67 nM. Ca2+i increased by 50 nM after 5-10 min of metabolic inhibition. Blebbing of the cell membrane was evident within 30 min. Ca2+i did not appreciably increase further until the time of cell death, when the loss of plasma membrane integrity allowed unimpeded influx of extracellular Ca2+.(ABSTRACT TRUNCATED AT 250 WORDS)